1. Field of the Invention
The present invention relates to an apparatus and methods for removing a restriction in a tubular. Particularly, embodiments of the present invention relate to apparatus and methods for milling a restricted drill shoe. More particularly, embodiments of the present invention relate to apparatus and methods for milling a restricted drill shoe coupled to an expanded tubular.
2. Background of the Related Art
In the oil and gas exploration and production industry, bores are drilled from surface to access subsurface hydrocarbon reservoirs. The bores are typically drilled in sections: a section of bore is drilled using drilling apparatus including a bit mounted on the end of a string; the drilling apparatus is pulled out of the bore; a section of bore-lining tubing is run into the “open” bore; and the tubing is then cemented or otherwise sealed in the bore by filling the annulus between the tubing and the bore wall with cement slurry. These drilling and lining steps are repeated until the bore is of the required length or depth. Clearly, this can be a time-consuming operation as to drill and line each bore section it is necessary to make up and then dismantle first a drill string and then a running string, both of which may be several thousand meters long.
Furthermore, with conventional bore-lining techniques, the outer diameter of each section of bore-lining tubing must be smaller than the inner diameter of the preceding tubing to enable the tubing to be run into the bore. Thus, a step-wise reduction in bore diameter occurs at the transition between each bore section. The reduction in available bore diameter limits the production capabilities of the well, restricts access to the well, and also requires the use of smaller diameter and thus generally less robust drilling apparatus in the lower portions of the well. A further disadvantage also arises in that the upper portions of the bore may have to be drilled to a relatively large diameter, in light of the numerous subsequent diameter reductions that must be accommodated, which increases drilling time and expense.
Some of these disadvantages may be overcome by the use of expandable bore lining tubing. Generally, the expandable tubular is run in through a section of existing tubing and then expanded to a larger diameter. In this respect, the size of the inner diameter may be substantially preserved.
The expandable tubular 10 typically includes a casing shoe 20 at its lower end such that the cementing operation may be performed. See FIG. 1. To continue drilling, the casing shoe 20 must be removed. However, because the casing shoe 20 is not expanded, a small portion 15 of the expandable tubular is also not expanded. See FIG. 2. This unexpanded portion 15 becomes a restriction in the wellbore and may pose a problem for continued drilling. This is because most drill bits adapted to drill the well are not suitable for drilling through the tubular's steel composition. One solution is to make two trips into the well. First, a bit or mill coupled to a reaming tool is run in to drill or mill out the restricted section. Then, a drilling assembly is run-in to deepen or drill the well.
There is a need, therefore, for apparatus and methods to remove a restriction in a well and drill another section of the well in a single trip. There is also a need for apparatus and methods to remove a drill shoe from an expanded tubular and extend the well in a single trip.